The thermodynamics of austenite
First order statistical model for temperature dependence of carbon activity in austenite
Dunn, W. W.↗
SEARCH · Engineering Papers
Results for “statistical models”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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A technique for assessing probable distributions of tropical precipitation echo lengths for X-band radar from Nimbus 3 HRIR data
Statistical model for simulating radar echoes from tropical precipitation for ocean surface region using Nimbus 3 satellite infrared data
Hudlow, M. D.↗
Computer discrimination procedures applicable to aerial and ERTS multispectral data
Two statistical models are compared in the classification of crops recorded on color aerial photographs. A theory of error ellipses is applied to the pattern recognition problem. An elliptical boundary condition classification model (EBC), useful for recognition of candidate patterns, evolves out of error ellipse theory. The EBC model is compared with the minimum distance to the mean (MDM) classification model in terms of pattern recognition ability. The pattern recognition results of both models are interpreted graphically using scatter diagrams to represent measurement space. Measurement space, for this report, is determined by optical density measurements collected from Kodak Ektachrome Infrared Aero Film 8443 (EIR). The EBC model is shown to be a significant improvement over the MDM model.
Richardson, A. J.↗
Photographic astrometry and overlap reduction techniques
Rigorous adjustment algorithms are discussed which extract hidden information contained in overlapping photographs of star fields. In particular, the development of adequate physical and statistical models is emphasized.
Googe, W. D.↗
Comments on the possibility for determining detailed atmospheric structure from transhorizon radio propagation measurements
A deterministic approach is used to examine the atmospheric structure at any instant in time, with an assumption as to the degree of anisotropy. A statistical model is also used to relate the experimental data to atmospheric structure. With this model, the three dimensional spectrum of spatial wave numbers of the refractivity fluctuations are determined, along with correlations which exist within the spectrum.
Kieburtz, R. B.↗
Computer identification of ground pattern from aerial photographs.
Two statistical models are comapared in the classification of crops recorded on color aerial photographs. A theory of error ellipses is applied to the pattern recognition problem. An elliptical boundary condition classification model (EBC), useful for recognition of candidate patterns, evolves out of error ellipse theory. The EBC model is compared with the minimum distance to the mean (MDM) classification model in terms of pattern recognition ability. The pattern recognition results of both models are interpreted graphically using scatter diagrams to represent measurement space. Measurement space, for this report, is determined by optical density measurements collected from Kodak Ektachrome Infrared Aero Film 8443 (EIR). The EBC model is shown to be a significant improvement over the MDM model.
Richardson, A. J.↗
Statistical distribution of spacecraft maximum structural response.
Under nonstationary random excitations resulting from booster engine shutdown, a direct statistical analysis of spacecraft maximum response is performed, and the spacecraft structural reliability is obtained. It is found that the Gumbel (1958) Type I asymptotic distribution of maximum values provides a reasonably good statistical model for spacecraft maximum responses. This approach makes it possible to perform the reliability-based optimum design of spacecraft structures.
Yang, J.-N.↗
Analysis of stress-rupture data from S-glass composites.
Both composite and free strands have been tested to study matrix effectiveness. Glass from different lots were used, and processing parameters were varied to demonstrate the effects of material variability. The statistical patterns that emerge from these experiments show that lifetime distributions are characteristically skewed. As a class, the lifetime distributions are well approximated by the reduced form of the Weibull distribution. The strength retention data display little early degradation. The retained-strength distributions can also be classed as Weibull distributions. A statistical model applied to the data gives predictions of progressive failure, strength retention path, and expected life for two basic types of internal fracture processes.
Robinson, E. Y.↗
Dynamics of meteor streams and new asteroid-meteor and comet-meteor associations
The orbital data on 19,303 meteors were analyzed in terms of the dynamics of meteor streams. A statistical model of meteor streams is discussed along with stream-search techniques, and associations of radio meteor streams with comets and minor planets.
Sekanina, Z.↗
Optical communication theory.
An introduction is provided to the important ideas involved in the design and the evaluation of optical communication systems which transmit digital or analog data. Field representations are discussed together with background noise, a detector statistical model, quantum receivers, and turbulent and scatter channels. Free-space channels are considered, taking into account heterodyne systems, preamplifier and homodyne systems, direct-detection systems, and optimum quantum systems.
Hoversten, E. V.↗
Far field effects of weak spatially periodic inhomogeneities.
Small variations in the properties of an acoustic medium produce cumulative effects that significantly alter wave forms propagating over long distances. To investigate some aspects of these effects, without statistical models, the one-dimensional wave equation with a weak spatially periodic variation in the sound speed is treated. An approximation is developed valid for such weak inhomogeneities over large distances based upon the approximate treatment of a linear differential equation with a periodic coefficient. It is applied to the propagation of an initial step wave and identifies the dispersive nature of the medium which accounts for the cumulative effects.
Friedman, M. B.↗
Regolith history from cosmic-ray-produced isotopes
A statistical model is given for soil development relating meteoroid impacts on the moon to cosmic-ray-produced isotopes in the soil. By means of this model, the average lunar mass loss rate during the past 1.4 aeons is determined to be 170g/sq cm aeon and the soil mixing rate to be approximately 200 cm/aeon from the gadolinium isotope data for the Apollo 15 and 16 drill stems. The isotope data also restrict the time variation of the meteoroid flux during the past 1.4 aeons.
Fireman, E. L.↗
A guidance and navigation system for continuous low thrust vehicles
A midcourse guidance and navigation system for continuous low thrust vehicles is described. A set of orbit elements, known as the equinoctial elements, are selected as the state variables. The uncertainties are modelled statistically by random vector and stochastic processes. The motion of the vehicle and the measurements are described by nonlinear stochastic differential and difference equations respectively. A minimum time nominal trajectory is defined and the equation of motion and the measurement equation are linearized about this nominal trajectory. An exponential cost criterion is constructed and a linear feedback guidance law is derived to control the thrusting direction of the engine. Using this guidance law, the vehicle will fly in a trajectory neighboring the nominal trajectory. The extended Kalman filter is used for state estimation. Finally a short mission using this system is simulated. The results indicate that this system is very efficient for short missions.
Tse, C. J. C.↗
Monte Carlo applications to acoustical field solutions
The Monte Carlo technique is proposed for the determination of the acoustical pressure-time history at chosen points in a partial enclosure, the central idea of this technique being the tracing of acoustical rays. A statistical model is formulated and an algorithm for pressure is developed, the conformity of which is examined by two approaches and is shown to give the known results. The concepts that are developed are applied to the determination of the transient field due to a sound source in a homogeneous medium in a rectangular enclosure with perfect reflecting walls, and the results are compared with those presented by Mintzer based on the Laplace transform approach, as well as with a normal mode solution.
Haviland, J. K.↗
The repulsive 1 Sigma g/+/ He2 potential obtained from total cross sections
An improved apparatus for obtaining short-range molecular potentials is described. The setup is a refined version of that used by Jordan-Amdur and by Leonas. The ion source is provided with a mass analyzing magnet, the capacitance manometer in the scattering cell is calibrated with a McCleod gauge, and the detection unit substitutes a Channeltron multiplier for the thermopile. The measured ground-state He-He potential for radii between 0.49 and 1.56 A is approximately V(r) = 215 x exp(-3.95r) eV, which is 25% higher than the earlier experiments. The result is supported by molecular orbital and statistical model calculations.
Foreman, P. B.↗
A guidance and navigation system for continuous low-thrust vehicles
A midcourse guidance and navigation system for continuous low thrust vehicles was developed. The equinoctial elements are the state variables. Uncertainties are modelled statistically by random vector and stochastic processes. The motion of the vehicle and the measurements are described by nonlinear stochastic differential and difference equations respectively. A minimum time trajectory is defined; equations of motion and measurements are linearized about this trajectory. An exponential cost criterion is constructed and a linear feedback quidance law is derived. An extended Kalman filter is used for state estimation. A short mission using this system is simulated. It is indicated that this system is efficient for short missions, but longer missions require accurate trajectory and ground based measurements.
Jack-Chingtse, C.↗
Inelastic scattering in atom-diatomic molecule collisions. I - Rotational transitions in the sudden approximation
The impact parameter method and the sudden approximation are applied to determine the total probability of inelastic rotational transitions arising from a collision of an atom and a homonuclear diatomic molecule at large impact parameters. An analytical approximation to this probability is found for conditions where the electron exchange or overlap forces dominate the scattering. An approximate upper bound to the range of impact parameters for which rotational scattering can be important is determined. In addition, an estimate of the total inelastic cross section is found at conditions for which a statistical model describes the scattering well. The results of this analysis are applied to Ar-O2 collisions and may be readily applied to other combinations of atoms and molecules.
Stallcop, J. R.↗
Hydrogen interactions with metals
Review of the literature on the nature and extent of hydrogen interactions with metals and the role of hydrogen in metal failure. The classification of hydrogen-containing systems is discussed, including such categories as covalent hydrides, volatile hydrides, polymeric hydrides, and transition metal hydride complexes. The use of electronegativity as a correlating parameter in determining hydride type is evaluated. A detailed study is made of the thermodynamics of metal-hydrogen systems, touching upon such aspects as hydrogen solubility, the positions occupied by hydrogen atoms within the solvent metal lattice, the derivation of thermodynamic functions of solid solutions from solubility data, and the construction of statistical models for hydrogen-metal solutions. A number of theories of hydrogen-metal bonding are reviewed, including the rigid-band model, the screened-proton model, and an approach employing the augmented plane wave method to solve the one-electron energy band problem. Finally, the mechanism of hydrogen embrittlement is investigated on the basis of literature data concerning stress effects and the kinetics of hydrogen transport to critical sites.
Mclellan, R. B.↗